As computer systems become more and more common in the workplace and in the home, the demand for transmission of information between these computer systems is increasing. Many computer system are interconnected through networks such as the Internet. Although each computer system connected to such a network can receive data from and send data to each other computer system, there are difficulties in using such networks. For example, because such computer systems are based on the telephone network, data transmission typically occurs at a relatively slow transmission rate. Also, when the same data is to be sent to multiple computer systems, the same data must be transmitted multiple times, that is, once for each computer system that is to receive the data.
When many computer systems need to receive the same data, some computer systems broadcast the data using satellite transmission. With satellite transmission, the same data can be sent only once and received by many computer systems. Although satellite transmission rates are very fast, there are several disadvantages of transmitting data by satellite. First, the cost of transmitting data by satellite can be prohibitive. Second, the cost of each computer system is increased because each computer system needs a satellite receiver. Third, if a computer system is not running at the time of transmission, the computer system cannot receive the transmission. Consequently, satellite transmissions are often repeated at periodic intervals to ensure that each computer system receives the transmission. Of course, the repeating of such transmissions can be expensive and may be unnecessary because all computer svstems, or least all those that care about the transmission, may have been running and actually received the data when it was first transmitted. Moreover, since such satellite transmissions typically only occur in one direction, there is generally no way of ensuring that all the intended recipient computer systems actually received a satellite transmission.
It would be desirable to have a transmission mechanism that would combine the advantages of the network computer systems and of satellite transmission, while minimizing their disadvantages.